In the production of a forged bicycle crank of the general type disclosed in U.S. Pat. No. 624,635, commonly an elongated steel rod is heated in a furnace and then manually and progressively transferred to a series of cavities formed with a forging die set. The die cavities provide for bending the rod to form a set of crank arms integrally connected by an axle portion. The axle portion is forged to form a cylindrical seat for a chain drive sprocket and to form a pair of enlarged cylindrical collars or bosses which are subsequently machined to retain the inner races of a set of anti-friction crank support bearings. The rod from which the crank is forged commonly has an original diameter slightly smaller than the diameter of the enlarged bosses but greater than the diameter of the rod portion between the bosses and the rod end portions which form the crank arms. As a result of the reduction in diameter of the rod to form the crank arms and the axle, the forged crank has a final overall length greater than that of the original steel rod.
It is also common in the forging of a bicycle crank to form a projecting sprocket engaging pin or stud on one of the crank arms as shown in the above patent to prevent rotation of the sprocket relative to the crank. U.S. Pat. No. 3,608,184 discloses another method for making a bicycle crank. In this patent, threads are rolled on the enlarged collars or bosses prior to bending the rod to form the crank arms, and a sprocket engaging pin or stud is then welded to one of the crank arms. However, this method presents a problem of possibly damaging the rolled threads during the bending and/or welding operation.
It has also been proposed to cold forge a bicycle crank by first reducing the diameter of one end portion of a metal rod and then forming one of the cylindrical bearing surfaces and the sprocket seat by a compression upset forming operation. The rod is then turned end-for-end, and the opposite end portion of the rod is reduced in diameter by a forging operation after which the second cylindrical bearing surface is formed by a compression upset forging operation. The rod is then bent to form the pedal crank arms, and a sprocket engaging stud is welded to one of the crank arms.